Properties of sustained and transient ganglion cells in the cat retina.

1. The functional basis for a sustained/transient classification of cat retinal ganglion cells has been strengthened by quantitative measurements of the sizes of the centre and surround components of receptive fields. Transient cells had larger surrounds than sustained; the distributions were non-overlapping.

Insertion of the F factor into the cluster of rfa (rough A) genes of Salmonella typhimurium.

From F(+) strains of Salmonella typhimurium, isolates were obtained representing two new classes of Hfr strains, HfrK1 and HfrK2, in which the insertion of the F factor into the rfa genes results in chromosome mobilization either clockwise or anticlockwise from rfa, and in the Rfa phenotype. The point of insertion of the F factor into the cluster of rfa genes, revealed by studies of the early transfer of their normal alleles, is as follows: xyl-cysE-rfa-657 (HfrK2-1, SA540 -->)-(<-- HfrK1-1, SA458)-rfaG-(<-- HfrK1-2, SA464)-pyrE-metA

P22-mediated transduction analysis of the rough A (rfa) region of the chromosome of Salmonella typhimurium.

Seven temperature-sensitive rough mutants of Salmonella typhimurium were found to be sensitive to smooth-specific phages at low temperature (25 C, 30 C) and resistant or partially resistant to rough-specific phages, whereas at high temperatures (37 C, 45 C) they were resistant or partially resistant to smooth-specific phages but sensitive to rough-specific phages. These data indicate that at low temperature each strain makes lipopolysaccharide which is relatively normal, but at high temperatures O-specific side chains are not added to the lipopolysaccharide. At 45 C, these strains have the R-res-1 or R-res-2 phage sensitivity phenotype, and their genetic lesions map by P22-mediated transduction in the rfa gene cluster between cysE-pyrE, suggesting a mutation in genes with transferase functions.

Hemin-deficient mutants of Salmonella typhimurium.

Nine hemin-deficient mutants of Salmonella typhimurium LT2 were isolated as neomycin-resistant colonies. Five of these mutants could be stimulated by Delta-aminolevulinic acid (Delta-ALA), thus representing hemA mutants. Since S.